Ignition composition



Jan. 18, 1938. L A BURROWS ET AL 2,105,635

IGNITION COMPOSITION Filed Oct. 30, 1935 WA. I I \5 Zawfon A/Burmws Wz'l/zam f. f1' /berf INVENTORS 2'. fm me! Reid ATTORNEY Patented Jan. 18, 1938 UNITED STATES PATENT OFFICE IGNITION COMPOSITION Wenonah, and William F.

J., and Ebenezer Emmet assignors to E. I. du Company, Wilmington,

Del., a corporation of Delaware Application October 30,

14 Claims.

The present invention relates to a new and improved ignition composition and more particularly to an ignition composition suitable for use in an electric blasting cap.

As is well known, blasting initiators consist essentially of a cylindrical shell or capsule containing a base charge of explosive material, an ignition composition superposed thereon and a firing means for initiating the ignition composition. On the basis of the firing means employed, these initiators are generally classified into two main types, namely: (1) electric blasting initiators, which employ an electric current to fire the ignition composition; and (2) ordinary blasting initiators which are initiated by a suitable length of safety fuse. Depending on the nature of the base charge employed these blasting initiators are further classified into (a) detonators or blasting caps, suitable for use with detonating or high explosives; and (b) igniters or squibs, adapted for use with defiagrating explosives.

The ignition compositions referred to in the foregoing should possess a number of definite properties to be satisfactory for general use. They should, for example, be easy to prepare, readily ignited, and burn with an intense flame. For certain rather special uses, as for example in electric blasting caps to be employed in seismic exploration, the ignition compositions should possess, in addition to the above mentioned properties, at very rapid rate of ignition.

The rate of ignition of an ignition composition exerts a controlling influence on the interval or time lag between the instant the firing current is applied and the instant the cap detonates. As more fully explained in copending application of Aughey, Burrows and Lawson, Serial No. 47,385 filed October 30, 1935 this overall time lag is the result of two separate factors. The first of these, which may be termed the bridge wire lag, is the interval between the application of the current and the fusion or breakin of the bridge wire. The second factor, hereinafter called the induction period, is the interval between the breaking of the bridge wire and the detonation of the cap. It is now well established that the bridge wire lag and the induction period are definite characteristic properties of each ignition composition, when a given firing current is employed.

The ignition compositions heretofore employed in electric blasting caps have not been altogether satisfactory from the point of view of 1935, Serial No. 47,387

speed. In the co-pending application above referred to, however, several new and improved ignition compositions are disclosed which possess no measurable "induction period, when fired with current at 12 amps. These compounds are therefore especially desirable for use in electric blasting caps for the special uses mentioned. It has been found, however, that some of these ignition compositions possess an undesirably high 10 firing current.

The object of the present invention is a new and improved ignition composition. A further object is an ignition composition which has a low firing current and a very rapid rate of ignition. 15 A still further object is an electric blasting cap which has a low firing current and a negligible induction period. Other objects will be apparent as the invention is hereinafter more fully described. 20

We have found that the above objects are realized by employing an ignition composition comprising a lead salt in which the lead is in its highest valence state. Thus, instead of using a divalent lead salt, we employ a tetravalent-lead 25 I salt. Preferably we employ an ignition composition comprising a salt of tetravalent lead, such as the alkyl lead salts of acidic substances of high energy content, as, for example, the alkyl'lead salts of an acidic explosive substance containing at least one replaceable acidic hydrogen atom. Many such explosive acidic substances may be employed, but we prefer to use substances of high nitrogen content which are soluble in aqueous alkali. Thus, for example, we 35 may form the alkyl lead salts of nitrotetrazole, azoaminotetrazole, or azidodithiocarbonic acid, all of which readily dissolve in alkali. We prefer, however, to employ the alkyl lead salts of hydrazoic orstyphnic acid. Other acidic explosive substances may of course be used in accordance with our invention, but the last mentioned acids are especially attractive from an economic viewpoint, and possess other advantageous properties.

Various tetravalent lead salts may be used in accordance with our invention. Thus, we may use the alkyl lead salts, as for example, ,the trialkyl lead, the dialkyl lead, or the basic dialkyl lead salts as desired. The alkyl groups may be 60 the same or different. Since, however, polyalkyl lead salts containing different alkyl groups are difiicult to prepare and moreover possess no distinct advantages over their more simple analogues, we prefer to use the polyalkyl lead salts 5 in which the alkyl groups are the same. Fur- EXAMPLE IV thermore since tetraethyl lead is now readily Mono-triethyl lead azo-amz'notetrazole available in large quantities, we prefer the polyethyl lead salts, such as, for example, the tri- N N ethyl lead, the'diethyl lead, and the basic diethyl lead salts of the acidic substances mentioned in f the foregoing. If

In order to describe our invention more clearly, Pkwmom),

we shall cite a number of examples of preferred embodiments thereof. It is to be understood, however, that this is done solely by way of example, and is not to be regarded as a limitation on the scope of our invention which has many important embodiments other than those hereinafter more particularly described.

EXAMPLE I 818- triethyl lead styphnate OPb-(CH:CH3)3 OaN NO;

Tetraethyl lead was treated with glacial acetic acid in the presence of silica gel, according to the directions of Browne and Reid (Jour. Amer. Chem. Soc. 49, 836 (1927)).

The resulting triethyl lead acetate was dissolved in dilute alcohol and the solution was treated with an'aqueous soution of the di-sodium salt of styphnic acid. The reaction mixture was digested for a few minutes at 60 C., during which time a yellow crystalline precipitate formed. The product was filtered and recrystallized from water. The yield was 75% of the theoretical based on the triethyl lead acetate employed. The explosion point was 204.

Analysis. Calculated for CisHaiosNsPBz; Pb:

49.8% Found; Pb=49.91%

EXAMPLE II Triethyl lead-basic lead styphnate OPb(CH:C.Ha)|

OPb-OH A dilute alcoholic solution of triethyl lead acetate was treated with an equivalent amount of the mono-sodium salt of styphnic acid in water, at W C. The resulting solution was made alkaline, and a slight excess of lead nitrate dissolved in water was added. A yellow precipitate formed at once. It was filtered, digested first with water, then with alcohol, and finally dried. The explosion point was 298 C.

Analysis: Calculated for CmHuOaNaPbz; Pb=

54.4% Found; Pb=54.10%

EXAMPLE III Triethyl lead azide (CH3CH2) sPb-Na Triethyl lead azide was prepared from triethyl lead acetate and sodium azide. The molten material detonated weakly on a hot plate.

This compound was obtained by the action of the mono-sodium salt of azo-aminotetrazole on triethyl lead acetate. It ignited without detonation, and had a firing current of 0.32-0.37 amp.

EXAMPLE V Bis-triethyl lead azo-aminotetrazole Triethyl lead azido-dz'thiocarbtmate (OlIaCHz)a-PbS ]Na This compound was prepared by the action of aqueous sodium azido-dithiocarbonate on triethyl lead acetate in about %"yield. It ignited without detonation.

EXAMPLE VII Diethyl lead diazz'de (CH3CH2) 2PbN6 Diethyl lead dichloride, (CHaCHa) PbClz, was prepared according to the method of Gilman and Robinson (Jour. Amer. Chem. Soc. 52, 1977 (1930)) and Griittner and Krause (Ber. 49, 1426 (1916)) from tetraethyl lead and chlorine. It was recrystallized from alcohol.

To an aqueous solution of diethyl lead dichloride an aqueous solution of soditun azide was added dropwise with stirring. The reaction mixture was warmed to 50 C. during the addition of the diethyl lead dichloride, after which the temperature was reduced to 25 C. The product was filtered, and washed with water, alcohol, and ether. It detonated with a bright flame on the hot plate.

Analysis." Calculated for C4H1oNsPb; Pb=59.4%

Found; Pb=59.6%

EXAMPLE VIII Bis-basic diethyl lead styphnate v of the simple lead salts, is

g 2 of tetryl, with a priming charge which separated had an explosion point of 229 C.

Analysis: Calculated for CmHzzUmNsPbz; PM:

51.2% Found: Pb=5l.2%

In all the above compounds, the lead has a valence of four. The eiiect of this increase in valence, by forming the alkyl lead salts instead clearly seen with reference to the following table which shows the firing current and speed characteristics of representative alkyl lead derivatives in comparison with the corresponding properties of lead styph nate which is cited as representative of the fastest ignition compositions heretofore disclosed in to be limited only in accordance with the following patent claims.

We claim:

1. An ignition composition for a blasting cap comprising an alkyl lead salt of a member of the the literature. group consisting of hydrazoic acid, azidodithiogggg fg g Bridge Induction Total (loose (cemented wire lag period at leg at charge) charge) at 12 amps. 12 amps. l 2 amps. amps. amps (in sees.) (in sees.) (111 secs.)

Lead styphnate 0. 0. -0. 47 0. 00020 0- 00020 Triethyl lead-basic le d styphnate 0. 3i 0. 36 0. 00020 0- 0002 Diethyl lead-diazidc 0. 35 0. 42 0.00052 0.00038 0. 0009 Bis-basic diethyl lead styphnato 0. 31 0. 36 0.00017 0- 000 7 It is apparent from the above table that the lead salts of tetravalent lead have firing currents which are from 10-27% less than those of the corresponding lead salts of divalent lead. This lowering of the firing current is accomplished without appreciable eiiect either on the induction period or the overall time lag, as indicated in the last two columns of the above table.

In order to describe the application of our invention to blasting initiators, we shall refer to the accompanying drawing which represents a vertical section of an electric blasting cap. Itis to be understood, however, that this is done solely by way of illustration, and is not to be regarded as a limitation upon the scope of our invention. It will be apparent to those skilled in the art that our ignition compositions may be employed either as loose or cemented compositions in all types of blasting initiators, including ordinary and electric blasting initiators, and in squibs. They may also be used in delay blasting caps, if desired.

Referring to the drawing, the blasting cap illustrated comprises a metallic shell or capsule l at the base of which is placed a secondary charge 3 of lead azide superposed thereon. In the cavity in the lower end of the plug 8 the ignition composition 4 is cemented around the bridge wire 5 and the ends of the two leg wires 6 and I, which are held in fixed space relationship by the bridge plug 8. The cap is closed by a waterproof composition 9 and a sulfur seal ii]. If desired, the firing circuit may be provided with a means for reducing the electrostatic susceptibility of the cap, comprising any of the means disclosed in co-pending application, Serial No. 47,385 filed October 30, 1935.

The ignition composition 4 may comprise any of the tetravalent-lead salts within the purview of this patent. Thus for example the composition may comprise bis-triethyl lead styphnate, diethyl lead diazide, bis-basic diethyl lead styphnate, mono-triethyl lead azo-amino-tetrazole, or in general, any alkyl lead salt of an acidic explosive .substance, as above described. We prefer, howcarbonic acid and styphnic acid, said lead being in the tetravalent state. a

2. The ignition composition of claim 1, in which said alkyl lead salt comprises an ethyl lead salt.

3. An ignition composition for a blasting cap comprising at least one member of the group consisting of the trialkyl lead, the dialkyl lead, and the basic dialkyl lead salts of an acidic explosive substance, said lead being in the tetravalent state.

4. The ignition composition of claim 3, in which said alkyl lead salt comprises an ethyl lead salt.

5. An ignition composition in an electric blasting cap comprising bis-triethyl lead styphnate.

6. An ignition composition in an electric blasting cap comprising triethyl lead-basic lead styphnate.

'7. An ignition composition in an electric blasting cap comprising bis-basic diethyl lead styphnate.

8. As anew compound, an alkyl lead salt of an acidic explosive substance containing at least 11. As a new compound, bis-triethyl lead styphnate.

12. As a new compound, triethyl lead-basiclead styphnate.

13. As a new compound, bis-basic diethyl lead styphnate.

14. An ignition composition comprising an alkyl lead salt which burns with explosive rapidity, said alkyl lead salt being a salt of an acidic explosive compound, and said lead being in the tetravalent state. 

